To many patients and aged people bed is necessary for rest and rehabilitation. Hence many nursing institutions have installed monitoring cameras to monitor whether the patients or aged people have rested on the beds timely to maintain good health and also to understand their sleeping quality and conditions. However, such a scheme makes the people under monitoring uncomfortable mentally and cannot rest easily and also feel intrusion of privacy.
With advances of medical and technology medical equipments have a great deal of improvements in recent years. Now some beds can be equipped with weight sensors on the bed board with four weighing means installed on four legs of the bed, then by calculating through a formula the gravity center location of the person lay on the bed can judge whether the person has left the bed or changed the posture. Such an approach free the bedridden people the uncomfortable feeling of being watched by the monitoring cameras. But the aforesaid technique of judging the posture alteration via deduction of change of the gravity center through a formula could result in a greater range of faulty judgment. It also provides insufficient information in terms of the positional conditions of the person lay on the bed.